1. Technical Field
The present invention relates to a semiconductor light-emitting device, and in particular, to a light-emitting diode (LED) formed by bonding a semiconductor light-emitting layer, which has been grown on a growth substrate, to a support substrate, and then removing the growth substrate.
2. Description of the Related Art
In the past, an LED (having a metal bonding (MB) structure) constituted by bonding of a semiconductor light-emitting layered structure grown on a growth substrate (or a temporary substrate) by a vapor phase growth method such as metal-organic chemical vapor deposition (MOCVD) to a conductive support substrate (or a permanent substrate) with a reflective mirror therebetween, and then removing the growth substrate, has been disclosed, for example, in Japanese Laid-Open Patent Application 2009-10359 (hereinafter, referred to as Patent Document 1). The reflecting mirror is provided to the opposite side from the light-extraction surface, to improve light-extraction output to the outside.
In an LED of the aforementioned bonding structure, the thickness of the semiconductor layers is thinner in comparison to chip size, as compared with an LED fabricated on a conductive growth substrate; and as current spread is predominantly in the horizontal direction (i.e., in-plane direction), it is therefore difficult for the current to spread. The light-emission efficiency of an LED is dependent upon the current density injected into the active layer. When the current density is high, the carriers injected into the active layer overflow, thereby reducing the number of carriers that contribute to light emission, creating the problem of diminished light-emission efficiency and a fall in the linearity of light-emission output with respect to current. An additional problem in terms of reliability arises in that localized current concentrations cause propagation of crystal defects due to electrical field concentrations, heat generation, and the like.
A configuration adopting a so-called counter electrode configuration, which has no overlap between the electrode on the light-extraction surface side and the electrode on the reflecting surface side in top view, in order to facilitate current spread in the horizontal direction, has also been disclosed (for example, Japanese Laid-Open Patent Application 2008-282851 (hereinafter Patent Document 2) or Japanese Laid-Open Patent Application 2011-165853 (hereinafter Patent Document 3).
Additionally, in Japanese Patent Publication 4230219 (hereinafter Patent Document 4), for example, there is disclosed a semiconductor light-emitting device in which mesas are formed on the semiconductor layer, utilizing reflection at the side surfaces of the mesas to improve the light-extraction efficiency. Additionally, Japanese Laid-Open Patent Application 2004-297095 (hereinafter Patent Document 5) discloses an electrode configuration of an element having an insulating substrate.